Sydnones as Masked Hydrazines for the Synthesis of 4‐Arylazo‐1,2‐dihydro‐pyrazol‐3‐one Derivatives

Abstract

A simple and convenient one‐pot synthesis of 4‐(4‐chlorophenylazo)‐5‐methyl‐2‐aryl‐1,2‐dihydro‐pyrazol‐3‐ones (4a–j) has been carried out from 3‐arylsydnones (3a–j) by reaction with 2‐(4‐chlorophenyl)‐hydrazono‐3‐oxo‐butyric acid ethyl ester (2b). The 3‐arylsydnones are used as masked hydrazines in this reaction. Similarly, the 4‐arylazo‐2‐(7‐hydroxy‐4‐methyl‐2‐oxo‐2H‐chromen‐8‐ylmethyl)‐5‐methyl‐1,2‐dihydro‐pyrazol‐3‐ones (7a–j) were synthesized from 3‐[(7‐acetoxy‐4‐methyl‐8‐methylene)coumaryl]sydnone (5). All the newly synthesized compounds exhibited antimicrobial activity greater than the reference drugs used.

Keywords:

• 3‐arylsydnones
• 4‐arylazo‐pyrazolones

Acknowledgments

We thank G. S. Puranik, retired professor of Organic Chemistry and former chairman, Department of Chemistry, Karnatak University, Dharwad, India, for encouragement and suggestions. Authors also thank Sophisticated Instruments Facility (SIF), Indian Institute of Science, Bangalore, and University Scientific Instrumentation Centre (USIC), Karnatak University, Dharwad, India, for providing spectral data.